Method of and apparatus for air classification



Aug. 9, 1966 H. HARTE ETAL 3,

METHOD OF AND APPARATUS FOR AIR CLASSIFICATION Filed Aug. 14, 1962 W 4WW 3 1 0 sw M M M M W United States Patent Claims. (Cl. 209136) Thisapplication is a continuation-in-part of my copending application SerialNo. 182,802 filed March 27, 1962.

The present invention relates to a method of and to an apparatus forseparating lighter particles ttrom heavier particles which form amixture with the lighter particles, and more particularly to a method ofand an apparatus for separating lighter particles trom heavier particlesin a plurality of consecutive stages. Still more particularly, theinvention relates to a method and to an apparatus especially suited forseparating tobacco leaves from tobacco stems and constitutingimprovements over the method and apparatus disclosed in said .copendingapplication.

It is an important object of my invention to provide a method ofseparating lighter particles fro-m heavier particles according to whichthe separation of lighter and heavier articles is carried out in aplurality of stages so that even such lighter particles which might havebeen entrained by or entrapped between the heavier particles during afirst stage can be separated from heavier particles in the next stage orstages of the operation.

Another object of the invention is to provide a method of the justoutlined characteristics according to which the separation of lighterand heavier particles may be regulated independently in each stage ofoperation so that the extent of separation may be adjusted in dependencyon the weight of lighter and/or heavier particles, on the percentage oflighter and/or heavier particles in the mixture, on the looseness orcompactness of the mixture, and on all other factors which might have abearing on the separating operation.

A further object of the invention is to provide a very simple andefiicient apparatus for the practice of my method.

An additional object of the invention is to provide an apparatus forseparating tobacco leaves from a mixture of tobacco leaves and tobaccostems which is constructed and assembled in such a way that the leavesseparated in consecutive stages of separating operation may be mergedinto a single stream prior to their withdrawal from the apparatus.

A concomitant object of the invention is to provide an apparatus of thejust outlined characteristics wherein the steams separated inconsecutive stages may be withdrawn at different points or at a singlepoint of the apparatus, depending upon whether the stems separated inconsecutive stages of operation do or do not contain tobacco leaves.

Stiil another object of the invention is to provide an apparatus or theabove described type which may be rapidly and conveniently adjusted forcontinuous and fully automatic separation of lighter particles frommixtures wherein the percentage of lighter particles may vary within arather wide range.

Wit-h the above objects in view, the invention resides in the provisionof a method of separating lighter particles from heavier particles whichform a mixture with the lighter particles, comprising the steps ofintroducing the mixture into an ascending and preferably inclinedprimary air stream which is strong enough to entrain the 3,2 6 5 ,2 10Patented August 9, 1 966 major part or all of the lighter particles butwhich is too weak to entrain all of the heavier particles so that themajor part of heavier particles is tree to descend by gravity .whereasthe major part of lighter particles ascends with the primary air streamand the remainder of the mixture tends to accumulate above such sect-ionof the primary air stream from which the majority of heavier particlesdescends by gravity, and transferring the remainder of the mixture fromthe primary air stream into an ascending secondary air stream which isstrong enough to entrain the lighter particles but which is too weak toentrain the heavier particles so that the heavier particles descend bygravity [whereas the lighter particles ascend with the secondary airstream and may be merged with lighter particles entrained by the primaryair stream. The heavier particles descending trom or in the primary andsecondary air stream may be mixed or they may be withdrawn separately ifdesired.

In one of its preferred forms, the apparatus for the practice of mymethod comprises a housing which defines a primary and a secondaryseparator chamber, supply duct means for admitting a mixture of lighterand heavier particles into the lower zone of the primary chambertogether with a primary air stream which permits the major part ofheavier particles to descend by gravity into the lower zone and whichentrains at least the major part of lighter particles and the remainderof heavier particles toward the upper zone oi? the primary chamber,transfer means provided in the proximity of the upper zones of thechambers and .defining aperture means between the chambers through whichthe remainder of heavier particles and some lighter particles may enterby gravity into the secondary chamber, pneumatic means for producing inthe secondary chamber a secondary air stream which entrains the lighterparticles into the upper zone and which permits gravitational descent ofheavier particles into the lower zone of the secondary chamber,evacuating means connected with the upper zones of the chambers forwithdrawing lighter particles therefrom, and take-off means forreceiving heavier particles from the lower zones of the chambers.

The novel features which are considered as characteristic of theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following detailed description of a specificembodiment with reference to the accompanying drawings, in which:

FIG. 1 is a perspective view of a separator which embodies one form ofmy invention, one side wall and a portion of the front wall of theseparator housing being broken away; and

FIG. 2 is a smaller scale side elevational view of a slightly modifiedseparator wherein the heavier particles are taken off by a pneumaticconveyer.

Referring now in greater detail to the drawings, and first to FIG. 1,there is shown a separator comprising a main frame 1 including ahorizontal top plate 8 which is supportingly connected with a separatorhousing 2. The housing communicates with a supply duct 3- which servesas a means for admitting a primary stream of air and a mixture oflighter and heavier particles into the lower zone of an upwardlyextending primary separator chamber 10. This lower zone of the chamber10 has two sections including a first section 3a which communicates withthe duct 3, and a second section 4 which serves as a take-off duct andthrough which heavier particles may be evacuated by gravity from theprimary separator chamber. The duct 4 accommodates an air lock hereshown as a rotary cell wheel 5 which is driven by an electric motor 6mounted on the supporting plate 8. The

by two side walls 2a, 2b.

lower portion 7 of the take-off duct 4 discharges heavier particles ontothe upper run of a horizontal take-off conveyer 80.

The chamber 10 is inclined with respect to a vertical plane and isbounded by an inclined unperforated rear or lower wall 11, by aperforated or slotted front or upper wall 12 which is spaced from therear wall 11, and It will be noted that the inclination of the upperwall 12 with respect to a vertical plane is less pronounced than theinclination of the lower wall 11 so that the width of the chamber 10increases in a direction upwardly and away from the lower zone 3a,

4 thereof. The upper end of the upper wall 12 is connected with anarcuate baflle plate 13 which cooperates with a spaced deflector plate14 to reduce the width of the upper zone 15 of the chamber 10, thisupper zone constituting an evacuating duct through which lighterparticles are removed from the housing 2. The deflector plate 14preferably constitutes an imaginary upward extension of the lower wall11.

In accordance with our invention, the deflector plate 14 is spaced fromthe upper end of the lower wall 11 to form therewith a passage or gapwhich accommodates a transfer means or air lock in the form of a rotarycell wheel 75, the latter driven by the output shaft of the motor 6. Thecasing 75a of this air lock extends between the side walls 2a, 2b andthe air lock discharges a mixture of heavier and lighter particles intoa secondary separator chamber 77 which is bounded by the side walls 2a,2b, by a third wall 76 which simultaneously constitutes the rear wall ofthe housing 2, and by a front wall or partition 11a which terminates atthe upper end of the lower wall 11 below the casing 75a. The upper zone77a of the chamber 77 serves as an evacuating duct through which lighterparticles separated from the mixture admitted by the air lock 75 areevacuated from the housing 2. It will be noted that the air lock 75provides a connecting aperture which permits inflow of particulatematter from the upper zone of the primary chamber 10 into the upper zoneof the secondary chamber 77 but which prevents flow of particulatematter in the opposite direction.

walls 11, 76 and by the side walls 2a, 2b. Both takeoff ducts extendthrough the supporting plate 8.

The evacuating duct 15 normally communicates with a tubular evacuatingelement 18 provided at the upper end of the housing 2 through whichlighter particles separated in the primary chamber 10 are withdrawn fromthe separator. The other evacuating duct 77a may communicate with asimilar tubular element 1812 which is parallel with and is scalable fromthe element 18. The elements 18, 18a form part of a pneumatic evacuatingconveyer which advances lighter particles to a further processingstation, not shown.

A vertical front wall 29 of the housing 2 extends from the duct 3 andall the way to the upper tubular element 18a and is formed with ahorizontal opening or slot 19 which is adjacent to the underside of theelement 18 and whose effective area is regulatable by a flap valve 20. Asimilar opening or slot 21 is provided in the top wall 16 of the housing2 between the rear wall 76 and the tubular element 18a, and theeflective area of this slot 21 is regulatable by a flap valve 22.

The underside of the tubular element 18 is perforated or apertured as at25, this underside extending between the baflle plate 13 and the frontwall 29. The walls 13, 29, the battle plate 13, the underside 25 of thetubular element 18, and the two side walls 2a, 2b define betweenthemselves an upwardly expanding compartment 30 which communicates withthe pneumatic conveyer 18, 18a and with the primary chamber 10. Thiscompartment 30 may discharge some air through the slot 19, depending onthe adjustment of the valve 20.

The upper edge portion of the deflector plate 14 which separates theevacuating ducts 15, 77a from each other extends toward the intake endof the pneumatic conveyer 18, 18a and carries a pivotable flap valve 84which may be adjusted to seal the tubular elements 18, 1811 from eachother or to provide a path for the flow of lighter particles from theelement 18 to the element 18a or vice versa. In addition, the flap 84may seal the duct 15 from the pneumatic conveyer when it is pivoted intosealing engagement with the baflle plate 13. A similar flap valve 85 ishinged to the top wall 16 and serves as a means for regulating the crosssectional area of the intake end of the tubular element 18a, i.e., thevalve 85 selectively permits or prevents flow of lighter particles fromthe duct 77a into the element 18a. The intake ends of the elements 18,18a are separated from each other by a wedgeshaped intermediate wallmember 18b which extends between the side walls 2a, 2b. The valves 84,85 serve as a means for regulating the discharge of lighter particlesfrom the chamber 10, 77 into the pneumatic conveyer 18, 18a.

An inverted V-shaped baflle 31, 32 is pivotable about a horizontal shaft33 whose ends are journalled in the side walls 2a, 2b. This baflle ishinged to the upper edge of the wall portion 3b bounding the section 3aand may be adjusted to change the cross-sectional area of the section3a.

In the separator of FIG. 1, the direction of flow of lighter and heavierparticles and of a mixture of such particles is shown by full-linearrows. Broken-line arrows indicate the flow of air. The separator isbased on the suction principle and operates in the following manner:

The duct 3 admits a primary air stream which contains a mixture ofheavierand lighter particulate matter. It is assumed that the mixtureconsists of tobacco leaves (lighter particles) and tobacco stems, andthe purpose of the separator is to remove from the mixture all or nearlyall stems so that the material evacuated through the pneumatic conveyer18, 18a consists mainly or exclusively of tobacco leaves.

The strength of the air stream flowing upwardly through the upperportion 3a of the duct 3 and into the lower portion of the primaryseparator chamber 10 is selected in such a way that the stream entrainsall tobacco leaves whereas at least some stems begin to descend bygravity and pass through the air lock 5 to be discharged through thelower portion 7 of the take-off duct 4 and onto the take-off conveyer80.

The apertured upper wall 12 permits escape of some air from the primaryair stream and such escaping air produces a pressure differential whichcauses flow from the chamber 10 into the compartment 30 and which tendsto maintain the ascending tobacco leaves in close proximity to theright-hand side of the upper wall 12, as viewed in FIG. 1. This pressuredifferential causes air flow through the perforations or slots of thewall 12, through the compartment 30, through the perforated underside 25of the tubular element 18, and into the pneumatic conveyer. If the valve20 is at least partially open, air deflected by suction may escape tothe atmosphere. The strength of the suctional force is selected in sucha way that the latter can counteract the gravity of tobacco leaves andthus prevents the leaves from descending through the air lock 5. Theinclined lower wall 11 guides heavier stems toward the air lock 5 andenables the latter to withdraw such stems from the chamber 10. It willbe noted that the compartment 30 provides with the perforated underside25 and/or with the slot 19 a path for the deflected air thus enablingthe maintenance of the major part of ascending lighter particles awayfrom the lower wall 11 and transfer means 75.

Certain heavier leaves and some lighter stems which have reached thebaffle plate 13 and are caused to impinge against the deflector plate 14will be slowed down sufliciently to descend into the range of the secondair lock 75 so that the latter transfers the mixture of such particlesinto the secondary chamber 77 wherein the leaves are caused to advanceinto the upper zone 77a under the action of an ascending secondary airstream which is produced by suction prevailing in the pneumaticconeveyer 18, 18a. This secondary air stream enters the lower zone ofthe chamber 77 through the passage 78a between the flap 78 and rear wall7 6, and thereupon flows upwardly toward the duct 77a and into thepneumatic conveyer where it merges with the primary air streamdownstream of the transfer means 75. On its way to the pneumaticconveyer, the secondary air stream entrains all or nearly all leaves butis too Weak to entrain the stems so that the stems may descend bygravity to pass through the duct 79 and onto the conveyer 81. The mainportion of the secondary chamber 77 is substantially vertical because itis bounded in part by the inner side of the vertical rear wall 76 and bythe substantially vertical partition 11a. If the operator desires, hemay prevent mixing of tobacco leaves which ascend through the evacuatingducts 15, 77a by adjusting the valves 84, 85 in such a way that theevacuating ducts are sealed from each other. The purpose of the valves20, 22, 78 and of the guide plate 32 is to regulate the strength of theprimary and secondary air streams and of the cross current in such a Waythat the particulate matter entering the pneumatic conveyer 18, 18a doesnot contain any stems and to prevent evacuation of tobacco leavesthrough the take-off ducts 4 and 79. The valves 22, 78 may adjust thestrength of the secondary air stream independently of the primary airstream.

The separator of FIG. 2 comprises a housing defining two takeoff ducts107, 179 which respectively correspond to the take-off ducts 4, 79 ofFIG. 1. The ducts 107, 179 discharge heavier particles through a singleopening 83 and into a common pneumatic take-off conveyer 82; otherwise,the construction of this apparatus is the same as that of the apparatusshown in FIG. 1.

FIG. 2 shows an adjusting arm 33a which is utilized for regulating theposition of the baffle 31, 32. The side wall 2a is provided with severalwindows 1100 which permit observation of the separating operation in thechambers 1t), 77 and in the general area of the transfer means 75.

We have found that the quantity of lighter particle removed from theoriginally introduced mixture by the primary air stream with or withoutthe help of a cross current normally approximates 25-30 percent of theoriginal mixture. The quantity of heavier particles withdrawn throughthe air lock 5 is about 30 percent of the originally admitted mixture sothat the second air lock 75 normally transfers between 40-45 percent ofthe original mixture into the secondary chamber 77. In the absence of asecondary air stream, nearly one-half of the original mixture would bewithdrawn from the separator without any separation of lighter particlesso that the efficiency of the separator would be extremely low. Thepurpose of the cross current flowing in the path defined by theapertured upper wall 12, by the compartment 30, by the perforatedunderside 25 and/or by the slot 19 is to assist the primary air streamin entraining the major part of lighter particles toward the upper zoneof the primary chamber and to reduce the capacity of heavier particles'to entrain lighter particles counter to the direction of flow of theprimary air stream.

It will be readily understood that the separator may be modified in anumber of ways without departing from. the spirit of my invention. Forexample, it is possible to construct the housing 2 in such a way thatthe mixture admitted to the secondary chamber 77 is subjected to theaction of a second cross current. Also, some material advancing towardthe evacuating duct 77a may be transferred into a third separatorchamber if necessary so that the separating operation is then carriedout in three stages. While the output of the separator chamber 77 is notexceptionally high, its eificiency is very satisfactory especially ifthe transfer means is provided close to or at the upper end of thischamber. Moreover, since the valves 22 and 78 permit regulation of thesecondary air stream independently of the primary air stream, thelifting force of the secondary air stream may be adjusted with utmostprecision to insure that only heavy particles descend through the duct79 or 179.

The pneumatic conveyor 18, 18a is preferably connected to the suctionside of a fan whose pressure side produces the primary air stream in amanner as disclosed in a copending application Serial No. 182,802 ofWaldeman Wochnowski et al., assigned to the same assignee.

FIG. 1 shows the valve 84 in a position in which the elements 18, 18aare sealed from each other.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featureswhich fairly constitute essential characteristics of the generic andspecific aspects of this invention and, therefore, such adaptationsshould and are intended to be comprehended within the meaning and rangeof equivalence of the following claims. v

What is claimed as new and desired to be secured by Letters Patent is:

1. An apparatus for separating lighter tobacco particles from heaviertobacco particles which form a mixture with the lighter particles,comprising a housing defining an inclined primary separator chamber anda secondary separator chamber, said housing comprising an inclinedinternal wall which constitutes the lower wall of said primary chamberand each of said chambers having a lower zone and an upper zone; supplyduct means for admitting the mixture into said primary chamber in theproximity of said lower zone thereof together with an ascending primaryair stream which permits the major part of heavier particles to descendby gravity into the lower zone and which causes lighter particles andthe remainder of heavier particles to ascend toward the upper zone ofsaid primary chamber whereby the remainder of heavier particles and someof the lighter particles tend to descend by gravity onto and advanceupwardly along said inclined lower wall; transfer means comprising anair lock provided in the proximity of said upper zone and defining insaid inclined lower wall a connecting aperture between said chambersthrough which the remainder of heavier particles and such lighterparticles which advance upwardly along said wall may descend by gravityinto said secondary chamber; means for producing in said secondarychamber an ascending secondary air stream which entrains lighterparticles into the upper zone and which permits heavier particles todescend by gravity into the lower zone of said secondary chamber;evacuating means communicating with said upper zone for withdrawinglighter particles from said chambers; and take-off means for receivingheavier particles from the lower zones of said chambers independently ofeach other.

2. An apparatus as set forth in claim 1, wherein the means for producingsaid secondary air stream is a pneumatic conveyor which is connectedwith said evacuating means.

3. An apparatus for separating lighter tobacco particles from heaviertobacco particles which form a mixture with the lighter particles,comprising a housing defining a primary separator chamber and asecondary separator chamber, each of said chambers having a lower zoneand an upper zone; supply duct means for admitting the mixture into saidprimary chamber in the proximity of said lower zone thereof togetherwith an ascending primary air stream which permits the major part ofheavier particles to descend by gravity into the lower zone and whichpermits lighter particles and the remainder of heavier particles toascend toward the upper zone of said primary chamber; transfer meanscomprising an air lock provided in the proximity of said upper zones anddefining aperture means between said chambers through which theremainder of heavier particles and some lighter particles enter bygravity into said secondary chamber; means for producing in saidsecondary chamber an ascending secondary air stream which entrainslighter particles into the upper zone and which permits heavierparticles to descend by gravity into the lower zone of said secondarychamber; valve means provided in said housing for regulating thestrength of one of said streams independently of the other stream;evacuating means connected with the upper zones of said chambers forwithdrawing lighter particles therefrom; and take-off means forreceiving heavier particles from the lower zones of said chambersindependently of each other.

4. An apparatus for separating lighter tobacco par ticles from heaviertobacco particles which form a mixture with the lighter particles,comprising a housing defining an inclined primary separator chamber anda secondary separator chamber, said housing comprising a first inclinedinternal wall which constitutes the lower wall of said primary chamberand a perforated second inclined internal wall which constitutes theupper wall of said primary chamber, each of said chambers having a lowerzone and an upper zone; supply duct means for admitting the mixture intosaid primary chamber in the proximity of said lower zone thereoftogether with an ascending primary air stream which permits the majorpart of heavier particles to descend by gravity into the lower zone andwhich causes lighter particles and the remainder of heavier particles toascend toward the upper zone of said primary chamber whereby the majorpart of lighter particles ascends along said upper wall and theremainder of heavier particles and some of the lighter particles tend todescend by gravity onto and advance upwardly along said inclined lowerwall; transfer means comprising an air lock provided in the proximity ofsaid upper zones and defining in said inclined lower wall a connectingaperture between said chambers through which the remainder of heavierparticles and such lighter particles which advance upwardly along saidwall may descend by gravity into said secondary chamber;

evacuating means communicating with said upper zones for withdrawinglighter particles from said chambers; and take-off means for receivingheavier particles from the lower zones of said chambers independently ofeach other.

5. A method of separating lighter tobacco particles from heavier tobaccoparticles which form a mixture with the lighter particles, comprisingthe steps of introducing the mixture of lighter and heavier particlesinto an ascending inclined first air stream having an upper and lowersurface said stream being strong enough to entrain the major part oflighter particles but too weak to entrain all heavier particles so thatthe major part of heavier particles descends by gravity, that the majorpart of lighter particles ascends with the first air stream and that theremainder of the mixture tends to accumulate above such section of saidstream from which the majority of heavier particles descends by gravitydeflecting a portion of said inclined first air stream from said uppersurface and at an angle to the direction of its ascent so as to create apressure differential that maintains the major part of said lighterparticles in said first air stream despite the tendency of the heavierparticles descending from said lower surface to entrain lighterparticles counter to the direction of flow of said first air stream;transferring the remainder of the mixture from said first stream into asecond ascending air stream which is stong enough to entrain the lighterparticles but which is too weak to entrain the heavier particles so thatthe heavier particles descend by gravity whereas the lighter particlesascend with the second air stream; and separately withdrawing heavierparticles from said first and second air streams.

6. An apparatus for separating lighter tobacco particles from heaviertobacco particles which form a mixture with the lighter particles,comprising a housing defining a primary separator chamber and asecondary separator chamber, each of said chambers having a lower zoneand an upper zone; supply duct means for admitting the mixture into saidprimary chamber in the proximity of said lower zone thereof togetherwith an ascending primary air stream which permits the major part ofheavier particles to descend by gravity into the lower zone and whichpermits lighter particles and the remainder of heavier particles toascend toward the upper zone of said primary chamber; transfer meansprovided in the proximity of said upper zones and defining aperturemeans between said chambers through which the remainder of heavierparticles and some lighter particles enter by gravity into saidsecondary chamber; an air lock provided in said aperture means; meansfor producing said primary air stream and for simultaneously producingin said secondary chamber an ascending secondary air stream whichentrains lighter particles into the upper zone and which permits heavierparticles to descend by gravity into the lower zone of said secondarychamber; evacuating means connected with the upper zones of saidchambers for withdrawing lighter particles therefrom; and take-off meansfor receiving heavier particles from the lower zones of said chambersindependently of each other.

7. An apparatus for separating lighter tobacco particles from a mixtureof lighter and heavier tobacco particles, comprising a housing definingan inclined primary separator chamber and a secondary separator chamber,said housing comprising an inclined internal wall which constitutes thelower wall of said primary chamber and each of said chambers having alower zone and an upper zone; supply duct means for admitting themixture into said primary chamber in the proximity of said lower zonethereof together with an ascending primary air stream which permits themajor part of heavier particles to descend by gravity into the lowerzone and which causes the lighter particles and the remainder of heavierparticles to ascend toward the upper zone of said primary chamberwhereby the remainder of heavier particles and some of the lighterparticles tend to descend by gravity onto and advance upwardly alongsaid inclined lower wall; transfer means comprising an air lock providedin the proximity of said upper zones and defining in said inclined lowerwall a connecting aperture through which the remainder of heavierparticles and such lighter particles which advance upwardly along saidwall may descend by gravity into said secondary chamber; a pneumaticconveyor for producing in said secondary chamber an ascending secondaryair stream which entrains lighter particles into the upper zone andwhich permits heavier particles to descend by gravity into the lowerzone of said secondary chamber; evacuating means connected with saidpneumatic conveyor and with said upper zones for withdrawing lighterparticles from said chambers, said evacuating means comprising a firstevacuating duct connected to and receiving lighter particles from theupper zone of said primary chamber, a second evacuating duct connectedto and receiving lighter particles from the upper zone of said secondarychamber, and a first and second tubular element respectively connectedto and receiving lighter particles from said first duct and second duct;and take-off means for receiving heavier particles from the lower zonesof said chambers.

8. An apparatus as set forth in claim 7, further comprising valve meansfor regulating the effective cross sectional area and the flow of airthrough at least one of said ducts.

9. An apparatus as set forth in claim 7, wherein said ducts haveportions which are adjacent to and communicate with each other andfurther comprising valve means for regulating the flow of particles andair between said portions of said ducts.

10. An apparatus for separating lighter tobacco particles from heaviertobacco particles which form a mixture with the lighter particles,comprising a housing defining an inclined primary separator chamber anda secondary separator chamber, said housing comprising a first inclinediternal wall which constitutes the lower wall of said primary chamberand a perforated second inclined internal wall which constitutes theupper wall of said primary chamber, each of said chambers having a lowerzone and an upper zone; supply duct means for admitting the mixture intosaid primary chamber in the prox imity of said lower zone thereoftogether with an ascending primary air stream which permits the majorpart of heavier particles to descend by gravity into the lower zone andwhich causes the lighter particles and the remainder of heavierparticles to ascend toward the upper zone of said primary chamberwhereby the major part of lighter particles ascends along said upperwall and the remainder of heavier particles and some of the lighterparticles tend to descend by gravity onto and advance upwardly alongsaid inclined lower wall; transfer means comprising an air lock providedin the proximity of said upper zone and defining in said inclined lowerwall, a connecting aperture between said chambers through which theremainder of heavier particles and such lighter particles which advanceupwardly along said lower wall may descend by gravity into saidsecondary chamber; means for producing a pressure differential at theopposite sides of said perforated upper wall so that some of saidprimary air stream is deflected so as to pass through said upper walland to maintain the major part of ascending lighter particles to closeproximity of said upper wall and away from said transfer means wherebysuch lighter particles enter the upper zone of said primary chamber;evacuating means communicating with said upper zones for withdrawinglighter particles from said chambers; and take-ofl? means for receivingheavier particles from the lower zone of said chambers independently ofeach other.

References Cited'by the Examiner UNITED STATES PATENTS HARRY B.THORNTON, Primary Examiner.

HERBERT L. MARTIN, Examiner.

5. A METHOD OF SEPARATING LIGHTER TOBACCO PARTICLES FROM HEAVIER TOBACCOPARTICLES WHICH FORM A MIXTURE WITH THE LIGHTER PARTICLES, COMPRISINGTHE STEPS OF INTRODUCING THE MIXTURE OF LIGHTER AND HEAVIER PARTICLESINTO AN ASCENDING INCLINED FIRST AIR STREAM HAVING AN UPPER AND LOWERSURFACE SAID STREAM BEING STRONG ENOUGH TO ENTRAIN THE MAJOR PART OFLIGHTER PARTICLES BUT TOO WEAK TO ENTRAIN ALL HEAVIER PARTICLES SO THATTHE MAJOR PART OF HEAVIER PARTICLES DESCENDS BY GRAVITY, THAT THE MAJORPART OF LIGHTER PARTICLES ASCENDS WITH THE FIRST AIR STREAM AND THAT THEREMAINDER OF THE MIXTURE TENDS TO ACCUMULATE ABOVE SUCH SECTION OF SAIDSTREAM FROM WHICH THE MAJORITY OF HEAVIER PARTICLES DESCENDS BY GRAVITYDEFLECTING A PORTION OF SAID INCLINED FIRST AIR STREAM FROM SAID UPPERSURFACE AND AT AN ANGLE TO THE DIRECTION OF